1. Field of Invention
This invention pertains to convective heat therapy blankets. More specifically, the present invention relates to a heat therapy blanket wherein heated air not directed to the patient is recirculated through the blanket to recapture heat, thereby reducing heat emitted into the surrounding environment and reducing the required capacity of the associated heater.
2. Description of the Related Art
In the field of patient warming, it is well known that hypothermia is of concern. Hypothermia has been defined as a condition of subnormal body temperature which presents serious consequences to the patient. It has been shown that a large percentage of surgical patients develop hypothermia. The hypothermic condition is brought on by many factors including anesthesia, the air conditioning of the operating room, and the infusion of cold blood, I-V solutions, or irrigating fluids. Outside an operating room, hypothermia can occur when an individual has had prolonged exposure to a hostile environment such as freezing rain, snow or bitter cold.
Regardless of the cause of hypothermia, the individual initially experiences extreme discomfort which can quickly lead to a life threatening situation. It is known that one suffering from hypothermia must be attended to quickly in order to avoid irreversible body temperature drop or even death. Simply wrapping a person suffering from hypothermia in a blanket is a solution which can provide some relief, the blanket helping to retain body heat. This results in a gradual warming of the body. However, this method is not always sufficient to overcome hypothermia. The ability of the body to produce sufficient heat in sufficient time may not be possible or feasible in certain situations. Additionally, use of a blanket during or after an operation in a hospital can be cumbersome. It may be difficult to fully cover the patient's body due to intravenous tubing and other life supporting equipment which physically hinders placement of the blanket.
Another method used for heat therapy is an inflatable blanket used to direct heated air to a patient. Typically, these are used for surgical patients to maintain body temperatures while undergoing surgical or other procedures. A concern that arises in the use of such is the direct contact of heated air with an open wound or other skin conditions. This is especially of concern when the heated air is contaminated.
Various devices have been developed for heat therapy. Typical of the art are those devices disclosed in the following U.S. Patents:
U. S. Pat. No.Inventor(s)Issue Date2,093,834R. S. GauglerSep. 21, 19374,572,188S. D. Augustine et al.Feb. 25, 19864,660,388G. J. Greene, Jr.Apr. 28, 19874,777,802S. FeherOct. 18, 19885,106,373S. D. Augustine et al.Apr. 21, 19925,184,612S. D. AugustineFeb. 9, 19935,300,102S. D. Augustine et al.Apr. 5, 19945,304,213L. D. Berke et al.Apr. 19, 19945,324,320S. D. Augustine et al.Jun. 28, 19945,336,250S. D. AugustineAug. 9, 19945,350,417S. D. AugustineSep. 27, 19945,405,371S. D. Augustine et al.Apr. 11, 1995
Of these patents, the '834 patent issued to Gaugler discloses a refrigerating apparatus including an air blanket and a heating or cooling unit. The air blanket is fabricated from three layers of material. The lower layer is provided as a sheet to be placed over the user. Between the first and second layers is defined a plurality of air ducts through which the air travels. The lower layer is air-permeable such to direct the air to the user. The upper layer is provided to limit the bulging of the second layer when air is injected through the air ducts. In one embodiment, the air blanket defines a U-shaped return duct between the second and upper layers blanket. The '834 device is also described as having an evaporator for use when cooling the user and a humidifier when heating the user, the evaporator and humidifier each being provided for controlling the humidity of the air being directed toward the user.
The remaining patents disclose various air blankets for directing temperature controlled air toward a person situated under the blanket. Generally, these devices include a bottom layer constructed to be air-permeable and a top layer fabricated from an air-impermeable material. The bottom layer may be fabricated from an air-impermeable material and provided with openings for the passage of air, or may be fabricated from an air-permeable material. Each blanket defines a series of baffles through which the air travels before being directed through the bottom layer.
With these devices, air not directed to the person is forced into the surrounding environment in which the blanket is utilized. In an operating room, the exhaust of heated air into the room is adverse to the medical professionals who are trying to remain cool. The need to keep the patient warm takes precedent over the need to keep the medical professionals cool. However, an ideal situation provides for the patient to be warmed without substantially effecting the temperature of the immediate surroundings.
Illustrated generically in FIGS. 1 and 2 is one embodiment similar to the above devices 10P. A lower sheet 24P is dimensioned to cover the patient and drape over the sides of the bed (not shown). An air-impermeable upper sheet 12P is fixed to the lower sheet 24P. Baffles 58P are defined between the upper and lower sheets 12P,24P in a conventional manner such as by sonic welding, sewing or the like. The lower sheet 24P may be fabricated from either an air-impermeable or an air-permeable material. In the instance of an air-impermeable lower sheet, openings 28P are defined in the lower sheet 24P in order to direct air onto the patient. In the embodiment where the lower sheet 24P is air-permeable, the air is directed through the material to the patient without requiring openings 28P.
Other devices are disclosed in European Patent No. 716,746 issued to R. V. Lee on Oct. 13, 1954. One embodiment of the '746 device disclosed by Lee is an air conditioning cover for use on beds. The device includes an air blanket fabricated from upper and lower sheets quilted together at intervals to accomplish air circulation between the sheets. An opening is defined at one end of the upper sheet to receive an inlet duct. The upper and lower sheets are fabricated from an air-permeable material such that air directed through the inlet duct and between the upper and lower sheets is then directed through the upper and lower sheets.